Many electronic circuits and components, deployed in the context of various applications, employ voltage-controlled oscillators (“VCOs”). A VCO circuit generates a reference output signal having a specific frequency, and the nominal operating frequency range of a practical VCO circuit is dictated by its design. In practice, manufacturing process variation may result in a measurable difference between the actual operating frequency and the nominal operating frequency of a VCO. The process variation can occur from wafer to wafer and over a single semiconductor wafer, where chips located near the edge of the wafer can have different operating characteristics than chips located near the center of the wafer. In some cases, the actual VCO operating frequency range may be out of specification for the particular application, thus resulting in scrapped chips and lower manufacturing yields.
Most circuits designed for network communication are configured to accommodate multi-standard and multi-rate data streams. These circuits utilize dual or multiple VCO circuits. In practical embodiments, all of the multiple VCO circuits remain active at all times, which inherently consumes a significant amount of power due to the need to reduce phase noise or jitter. Such operation results in a waste of power when only one VCO need be active at any given time.
Prior art applications may employ multiple “always active” VCO circuits having multiplexed output signals. Cross-coupling between the multiple VCO output signals can be problematic, especially for high frequency applications. Unwanted cross-coupling results in a noisy VCO output signal.
Accordingly, a need exists for a VCO structure that addresses the above shortcomings and disadvantages of the prior art.